1. Field of the Invention
This invention relates to friction material such as used in brake blocks, brake linings and pads in vehicle braking systems.
2. Description of the Prior Art
The prior art friction materials have typically included asbestos fibers, phenolic resins, cashew nut shell oil particles, rubber particles, fillers, and ferrous or non ferrous metallic particles. The cashew oil based friction particles were usually cashew nut shell oil reacted with an aldehyde to form a thermoset material, the oil after heat treating for bodying and to remove the toxidity has also been used as a liquid binder in brake linings and disc brake pads. The thermoset material in particle form has been used extensively in most friction material compounds and usually in a weight percentage range of from 1% to 15%.
The present invention utilizes a processed mineral fiber formed of blast furnace slag such as known in the art as spun slag. The spun slag fibers replace the cashew oil based friction particles in substantially the same weight percentage range as the cashew nut shell oil in fusible thermoset particles heretofore referred to and result in a friction material yielding friction levels and wear characteristics equivalent to or better than prior art materials. The formation of the improved friction material is less costly and time consuming with the spun slag fibers than the comparable material utilizing the cashew oil based particles of the prior art and the relatively inexpensively formed spun slag fibers are available on the domestic market and free the friction material industry from reliance on unstable volume availability and price instability which has characterized the cashew nut shell oil of the prior art.
Typical prior art patents include the following: U.S. Pat. No. 3,227,249 of Jan. 4, 1966 discloses a molded composition brake shoe, a typical friction material, in which cashew nut shell liquid resin known as cashew polymer was present.
U.S. Pat. No. 3,959,149 discloses a brake shoe material in which cashew nut oil particles were present.
Both of these prior art patents disclose compositions dependent on the presence of the cashew nut shell oil resin and/or cashew nut shell oil particles. The present invention has no cashew nut shell oil based resins or particles and utilizes fibers spun from blast furnace slag which improve the wear characteristics and the frictional performance of the friction materials incorporating the same.